1. Field of the Invention
The present invention relates to a process of producing a one-piece intraocular lens in which an optical portion and a support portion of the lens are produced integrally and simultaneously with each other, wherein the optical and support portions are formed of different materials.
2. Related Art Statement
An intraocular lens includes an optical portion serving as an optical lens, and a support portion for attaching the optical portion to a suitable site in an eye of a patient. Conventionally, there are known intraocular lenses having two- or three-pieces in which an optical portion and a support portion are produced separately from each other and subsequently the support portion is fixed to the optical portion. Further, one-piece intraocular lenses are known in which an optical portion and a support portion are produced integrally with each other.
In addition, there is well known in the art an intraocular lens of a type in which an optical portion and a support portion are formed of different materials. For example, the optical and support portions are produced by polymerization of different monomer compositions including different polymerizable monomers, different compounding agents and/or additive agents, or different amounts of those agents. More specifically, the optical portion may be formed of a colorless, transparent polymerizable material and simultaneously the support portion may be formed of a polymerizable material containing a coloring agent, so that the support portion can easily be identified when the intraocular lens is inserted to patient's eye. In addition, it is known to add different amounts of crosslinking agent to respective materials for optical and support portions of an intraocular lens to provide different degrees of flexibility for the two portions. In this way, the optical and support portions possess different optical or physical properties with respect to each other as required.
Japanese Patent Application laid open under Publication No. 2-7954 ( corresponding to U.S. patent application No. 07/164,140) discloses a process of producing a one-piece intraocular lens wherein the optical and support portions thereof are formed of different materials. More specifically, the Japanese document teaches a process of producing an intraocular lens in which only the support portion thereof is colored. In the disclosed process, first, a colorless, transparent plastic material is used to provide a central portion for a lens blank. Subsequently a liquid, colored plastic material, is located around the central colorless portion, and then is polymerized to harden the outer colored portion. Thus, a lens blank is produced in which the central colorless portion and the outer colored portion are integrally combined with each other. Alternatively, a colored material first is formed into an outer portion for a lens blank and subsequently a colorless transparent material is poured into a central hole of the colored portion and is then polymerized, so as to produce a lens blank similar to the above-indicated first lens blank (i.e. lens blank in which the colorless central and colored outer portions thereof are integrally connected with each other). A desired intraocular lens is obtained by forming the colorless central and colored outer portions of the lens blank into the optical and support portions of the lens, respectively.
However, the above-indicated second process, in which the central portion of a lens blank is formed within a central hole in the colored outer portion, may suffer from a problem that distortion occurs to the central portion thus formed. That is, the optical properties of an intraocular lens as an end product may adversely be affected. Meanwhile, the above-indicated first process, in which the colored outer portion of a lens blank is formed by polymerization around the colorless central portion, may suffer from a problem that it is extremely difficult to align the center of the colorless central portion with the center of the lens blank as a whole. This problem causes the "color misalignment" problem that an intraocular lens as an end product has colored material in the optical portion or has colorless material in the support portion, because the lens blank is worked or machined into the lens by referencing the center of the entire lens blank as the center for the shape working.
Another process of producing a one piece-type intraocular lens whose support portion is colored, is disclosed in Japanese Patent Application laid open under Publication No. 62-161360 (corresponding to U.S. patent application No. 06/787,495). In the disclosed process, a colored plastic material is located around an optical member formed of a colorless transparent plastic material, and subsequently heat is applied to fuse the optical member and the plastic material into an integral member, that is, a lens blank. A final lens is obtained from this lens blank. This process may suffer from the problem that it is very difficult to align the center of the optical member with the center of the entire lens blank (i.e., the above-identified "color misalignment" problem).
As is understood from the foregoing description, the conventional processes have the problem that the optical properties of an intraocular lens produced thereby are deteriorated due to distortion occurring to the optical portion of the lens, or invasion of the material for the support portion of the lens into that for the optical portion thereof. In addition, the known processes suffer from the problem that the support portion of an intraocular lens fails to have satisfactory physical properties due to invasion of the material for the optical portion of the lens into that for the support portion.